When a patient suffers a wound to the body, the typical symptoms of inflammation include change of color (erythema), swelling (oedema), local increase in temperature and pain. Most of these symptoms result from changes in blood vessels caused by the release of inflammatory agents at the location of the damaged cells.
From a diagnostic point of view, change of color is one of the most important manifestations of inflammation.
Although the wound healing process is well documented from a physio-chemical perspective, physicians generally base the progress of the healing process on a visual observation of wound color and size. Judgement of changes in the wound is thus subjective, depending on a recollection of the earlier visual appearance of the wound.
A wound is defined as an area of tissue damage typically caused by the impact of a sharp object which may also cause breakage of the skin. The wound is not the total area of erythema, nor is it the erythema resulting from other causes such as an infection.
It is important to detect symptoms of potential complications as soon as possible so that appropriate treatment may be introduced to curtail further development of the complication, which may include infection.
Image processing techniques have been used to track variations in erythema over time. Images of the wound are captured at successive time intervals and processed in color spaces such as CIE L*a*b* for pseudo-perceptual image interpretation. The image is segmented using color to differentiate the erythema and the clear skin. The problem with this approach is the low contrast between the erythema and clear skin at the erythema boundary, which makes it difficult to obtain an accurate segmentation.
Another method of monitoring blood-flow changes such as those causing erythema is laser Doppler flowmetry. However, a laser Doppler perfusion imager (LDPI) registers blood flow only at a single point, so it takes several minutes to build up an image of the entire area of the wound. The method is time consuming compared to image-based techniques, and may inconvenience the patient.
There is accordingly a need for a simple, standardised method of quantifying the extent of erythema.